Harmonized design for intra bi-prediction and multiple reference line selection

ABSTRACT

Methods, apparatus, and computer readable storage medium for intra bi-prediction and multiple reference line intra prediction in video decoding. The method includes receiving, by a device, a coded video bitstream for a block. The method also includes determining, by the device, whether a single directional intra prediction or an intra bi-prediction applies to the block, based on mode information of the block, the mode information of the block comprising at least one of: a reference line index of the block, an intra prediction mode of the block, and a size of the block; in response to determining that the single directional intra prediction applies to the block, performing, by the device, the single directional intra prediction to the block; and in response to determining that the intra bi-prediction applies to the block, performing, by the device, the intra bi-prediction to the block.

RELATED APPLICATION

This application is a based on and claims the benefit of priority toU.S. Provisional Application No. 63/215,888 filed on Jun. 28, 2021,which is herein incorporated by reference in its entirety.

FIELD OF THE TECHNOLOGY

The present disclosure relates to video coding and/or decodingtechnologies, and in particular, to improved design and signaling ofintra bi-prediction and multiple reference line selection scheme.

BACKGROUND OF THE DISCLOSURE

This background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing of thisapplication, are neither expressly nor impliedly admitted as prior artagainst the present disclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, with each picture having a spatialdimension of, for example, 1920×1080 luminance samples and associatedfull or subsampled chrominance samples. The series of pictures can havea fixed or variable picture rate (alternatively referred to as framerate) of, for example, 60 pictures per second or 60 frames per second.Uncompressed video has specific bitrate requirements for streaming ordata processing. For example, video with a pixel resolution of1920×1080, a frame rate of 60 frames/second, and a chroma subsampling of4:2:0 at 8 bit per pixel per color channel requires close to 1.5 Gbit/sbandwidth. An hour of such video requires more than 600 GBytes ofstorage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the uncompressed input video signal, through compression.Compression can help reduce the aforementioned bandwidth and/or storagespace requirements, in some cases, by two orders of magnitude or more.Both lossless compression and lossy compression, as well as acombination thereof can be employed. Lossless compression refers totechniques where an exact copy of the original signal can bereconstructed from the compressed original signal via a decodingprocess. Lossy compression refers to coding/decoding process whereoriginal video information is not fully retained during coding and notfully recoverable during decoding. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is made smallenough to render the reconstructed signal useful for the intendedapplication albeit some information loss. In the case of video, lossycompression is widely employed in many applications. The amount oftolerable distortion depends on the application. For example, users ofcertain consumer video streaming applications may tolerate higherdistortion than users of cinematic or television broadcastingapplications. The compression ratio achievable by a particular codingalgorithm can be selected or adjusted to reflect various distortiontolerance: higher tolerable distortion generally allows for codingalgorithms that yield higher losses and higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories and steps, including, for example, motion compensation,Fourier transform, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, a picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be referred to as an intra picture. Intra pictures and theirderivatives such as independent decoder refresh pictures, can be used toreset the decoder state and can, therefore, be used as the first picturein a coded video bitstream and a video session, or as a still image. Thesamples of a block after intra prediction can then be subject to atransform into frequency domain, and the transform coefficients sogenerated can be quantized before entropy coding. Intra predictionrepresents a technique that minimizes sample values in the pre-transformdomain. In some cases, the smaller the DC value after a transform is,and the smaller the AC coefficients are, the fewer the bits that arerequired at a given quantization step size to represent the block afterentropy coding.

Traditional intra coding such as that known from, for example, MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt coding/decoding of blocks based on, for example, surroundingsample data and/or metadata that are obtained during the encoding and/ordecoding of spatially neighboring, and that precede in decoding orderthe blocks of data being intra coded or decoded. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction uses reference data only from the currentpicture under reconstruction and not from other reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques are available in a given video coding technology,the technique in use can be referred to as an intra prediction mode. Oneor more intra prediction modes may be provided in a particular codec. Incertain cases, modes can have submodes and/or may be associated withvarious parameters, and mode/submode information and intra codingparameters for blocks of video can be coded individually or collectivelyincluded in mode codewords. Which codeword to use for a given mode,submode, and/or parameter combination can have an impact in the codingefficiency gain through intra prediction, and so can the entropy codingtechnology used to translate the codewords into a bitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). Generally, for intra prediction, a predictor block can be formedusing neighboring sample values that have become available. For example,available values of particular set of neighboring samples along certaindirection and/or lines may be copied into the predictor block. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions specified in H.265's 33 possible intra predictordirections (corresponding to the 33 angular modes of the 35 intra modesspecified in H.265). The point where the arrows converge (101)represents the sample being predicted. The arrows represent thedirection from which neighboring samples are used to predict the sampleat 101. For example, arrow (102) indicates that sample (101) ispredicted from a neighboring sample or samples to the upper right, at a45 degree angle from the horizontal direction. Similarly, arrow (103)indicates that sample (101) is predicted from a neighboring sample orsamples to the lower left of sample (101), in a 22.5 degree angle fromthe horizontal direction.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are example referencesamples that follow a similar numbering scheme. A reference sample islabelled with an R, its Y position (e.g., row index) and X position(column index) relative to block (104). In both H.264 and H.265,prediction samples adjacently neighboring the block under reconstructionare used.

Intra picture prediction of block 104 may begin by copying referencesample values from the neighboring samples according to a signaledprediction direction. For example, assuming that the coded videobitstream includes signaling that, for this block 104, indicates aprediction direction of arrow (102)—that is, samples are predicted froma prediction sample or samples to the upper right, at a 45-degree anglefrom the horizontal direction. In such a case, samples S41, S32, S23,and S14 are predicted from the same reference sample R05. Sample S44 isthen predicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has continued to develop. In H.264 (year 2003), for example,nine different direction are available for intra prediction. Thatincreased to 33 in H.265 (year 2013), and JEM/VVC/BMS, at the time ofthis disclosure, can support up to 65 directions. Experimental studieshave been conducted to help identify the most suitable intra predictiondirections, and certain techniques in the entropy coding may be used toencode those most suitable directions in a small number of bits,accepting a certain bit penalty for directions. Further, the directionsthemselves can sometimes be predicted from neighboring directions usedin the intra prediction of the neighboring blocks that have beendecoded.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions in various encoding technologies developed overtime.

The manner for mapping of bits representing intra prediction directionsto the prediction directions in the coded video bitstream may vary fromvideo coding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions for intro prediction that arestatistically less likely to occur in video content than certain otherdirections. As the goal of video compression is the reduction ofredundancy, those less likely directions will, in a well-designed videocoding technology, may be represented by a larger number of bits thanmore likely directions.

Inter picture prediction, or inter prediction may be based on motioncompensation. In motion compensation, sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), may be used for a prediction of a newly reconstructedpicture or picture part (e.g., a block). In some cases, the referencepicture can be the same as the picture currently under reconstruction.MVs may have two dimensions X and Y, or three dimensions, with the thirddimension being an indication of the reference picture in use (akin to atime dimension).

In some video compression techniques, a current MV applicable to acertain area of sample data can be predicted from other MVs, for examplefrom those other MVs that are related to other areas of the sample datathat are spatially adjacent to the area under reconstruction and precedethe current MV in decoding order. Doing so can substantially reduce theoverall amount of data required for coding the MVs by relying onremoving redundancy in correlated MVs, thereby increasing compressionefficiency. MV prediction can work effectively, for example, becausewhen coding an input video signal derived from a camera (known asnatural video) there is a statistical likelihood that areas larger thanthe area to which a single MV is applicable move in a similar directionin the video sequence and, therefore, can in some cases be predictedusing a similar motion vector derived from MVs of neighboring area. Thatresults in the actual MV for a given area to be similar or identical tothe MV predicted from the surrounding MVs. Such an MV in turn may berepresented, after entropy coding, in a smaller number of bits than whatwould be used if the MV is coded directly rather than predicted from theneighboring MV(s). In some cases, MV prediction can be an example oflossless compression of a signal (namely: the MVs) derived from theoriginal signal (namely: the sample stream). In other cases, MVprediction itself can be lossy, for example because of rounding errorswhen calculating a predictor from several surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 specifies, described below is atechnique henceforth referred to as “spatial merge”.

Specifically, referring to FIG. 2 , a current block (201) comprisessamples that have been found by the encoder during the motion searchprocess to be predictable from a previous block of the same size thathas been spatially shifted. Instead of coding that MV directly, the MVcan be derived from metadata associated with one or more referencepictures, for example from the most recent (in decoding order) referencepicture, using the MV associated with either one of five surroundingsamples, denoted A0, A1, and B0, B1, B2 (202 through 206, respectively).In H.265, the MV prediction can use predictors from the same referencepicture that the neighboring block uses.

SUMMARY

The present disclosure describes various embodiments of methods,apparatus, and computer-readable storage medium for video encodingand/or decoding.

According to one aspect, an embodiment of the present disclosureprovides a method for intra bi-prediction and multiple reference lineintra prediction in video decoding. The method includes receiving, by adevice, a coded video bitstream for a block. The device includes amemory storing instructions and a processor in communication with thememory. The method also includes determining, by the device, whether asingle directional intra prediction or an intra bi-prediction applies tothe block based on mode information of the block, the mode informationof the block comprising at least one of a reference line index of theblock, an intra prediction mode of the block, and a size of the block;in response to determining that the single directional intra predictionapplies to the block, performing, by the device, the single directionalintra prediction to the block; and in response to determining that theintra bi-prediction applies to the block, performing, by the device, theintra bi-prediction to the block.

According to another aspect, an embodiment of the present disclosureprovides an apparatus for video encoding and/or decoding. The apparatusincludes a memory storing instructions; and a processor in communicationwith the memory. When the processor executes the instructions, theprocessor is configured to cause the apparatus to perform the abovemethods for video decoding and/or encoding.

In another aspect, an embodiment of the present disclosure providesnon-transitory computer-readable mediums storing instructions which whenexecuted by a computer for video decoding and/or encoding cause thecomputer to perform the above methods for video decoding and/orencoding.

The above and other aspects and their implementations are described ingreater detail in the drawings, the descriptions, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings.

FIG. 1A shows a schematic illustration of an exemplary subset of intraprediction directional modes.

FIG. 1B shows an illustration of exemplary intra prediction directions.

FIG. 2 shows a schematic illustration of a current block and itssurrounding spatial merge candidates for motion vector prediction in oneexample.

FIG. 3 shows a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an example embodiment.

FIG. 4 shows a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an example embodiment.

FIG. 5 shows a schematic illustration of a simplified block diagram of avideo decoder in accordance with an example embodiment.

FIG. 6 shows a schematic illustration of a simplified block diagram of avideo encoder in accordance with an example embodiment.

FIG. 7 shows a block diagram of a video encoder in accordance withanother example embodiment.

FIG. 8 shows a block diagram of a video decoder in accordance withanother example embodiment.

FIG. 9 shows directional intra prediction modes according to exampleembodiments of the disclosure.

FIG. 10 shows non-directional intra prediction modes according toexample embodiments of the disclosure.

FIG. 11 shows recursive intra prediction modes according to exampleembodiments of the disclosure.

FIG. 12 shows an intra prediction scheme based on various referencelines according to example embodiments of the disclosure.

FIG. 13A shows an intra bi-prediction according to example embodimentsof the disclosure.

FIG. 13B shows another intra bi-prediction according to exampleembodiments of the disclosure.

FIG. 14 shows a flow diagram of a method according to an exampleembodiment of the disclosure.

FIG. 15 shows an intra bi-prediction based on multiple reference linesaccording to example embodiments of the disclosure.

FIG. 16 shows another intra bi-prediction based on multiple referencelines according to example embodiments of the disclosure.

FIG. 17 shows a schematic illustration of a computer system inaccordance with example embodiments of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The invention will now be described in detail hereinafter with referenceto the accompanied drawings, which form a part of the present invention,and which show, by way of illustration, specific examples ofembodiments. Please note that the invention may, however, be embodied ina variety of different forms and, therefore, the covered or claimedsubject matter is intended to be construed as not being limited to anyof the embodiments to be set forth below. Please also note that theinvention may be embodied as methods, devices, components, or systems.Accordingly, embodiments of the invention may, for example, take theform of hardware, software, firmware or any combination thereof.

Throughout the specification and claims, terms may have nuanced meaningssuggested or implied in context beyond an explicitly stated meaning. Thephrase “in one embodiment” or “in some embodiments” as used herein doesnot necessarily refer to the same embodiment and the phrase “in anotherembodiment” or “in other embodiments” as used herein does notnecessarily refer to a different embodiment. Likewise, the phrase “inone implementation” or “in some implementations” as used herein does notnecessarily refer to the same implementation and the phrase “in anotherimplementation” or “in other implementations” as used herein does notnecessarily refer to a different implementation. It is intended, forexample, that claimed subject matter includes combinations of exemplaryembodiments/implementations in whole or in part.

In general, terminology may be understood at least in part from usage incontext. For example, terms, such as “and”, “or”, or “and/or,” as usedherein may include a variety of meanings that may depend at least inpart upon the context in which such terms are used. Typically, “or” ifused to associate a list, such as A, B or C, is intended to mean A, B,and C, here used in the inclusive sense, as well as A, B or C, here usedin the exclusive sense. In addition, the term “one or more” or “at leastone” as used herein, depending at least in part upon context, may beused to describe any feature, structure, or characteristic in a singularsense or may be used to describe combinations of features, structures orcharacteristics in a plural sense. Similarly, terms, such as “a”, “an”,or “the”, again, may be understood to convey a singular usage or toconvey a plural usage, depending at least in part upon context. Inaddition, the term “based on” or “determined by” may be understood asnot necessarily intended to convey an exclusive set of factors and may,instead, allow for existence of additional factors not necessarilyexpressly described, again, depending at least in part on context.

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the example of FIG. 3 , the first pair of terminal devices (310) and(320) may perform unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., of a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display the video pictures according tothe recovered video data. Unidirectional data transmission may beimplemented in media serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that perform bidirectionaltransmission of coded video data that may be implemented, for example,during a videoconferencing application. For bidirectional transmissionof data, in an example, each terminal device of the terminal devices(330) and (340) may code video data (e.g., of a stream of video picturesthat are captured by the terminal device) for transmission to the otherterminal device of the terminal devices (330) and (340) via the network(350). Each terminal device of the terminal devices (330) and (340) alsomay receive the coded video data transmitted by the other terminaldevice of the terminal devices (330) and (340), and may decode the codedvideo data to recover the video pictures and may display the videopictures at an accessible display device according to the recoveredvideo data.

In the example of FIG. 3 , the terminal devices (310), (320), (330) and(340) may be implemented as servers, personal computers and smart phonesbut the applicability of the underlying principles of the presentdisclosure may not be so limited. Embodiments of the present disclosuremay be implemented in desktop computers, laptop computers, tabletcomputers, media players, wearable computers, dedicated videoconferencing equipment, and/or the like. The network (350) representsany number or types of networks that convey coded video data among theterminal devices (310), (320), (330) and (340), including for examplewireline (wired) and/or wireless communication networks. Thecommunication network (350) may exchange data in circuit-switched,packet-switched, and/or other types of channels. Representative networksinclude telecommunications networks, local area networks, wide areanetworks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (350) may beimmaterial to the operation of the present disclosure unless explicitlyexplained herein.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, a placement of a video encoder and a video decoder in avideo streaming environment. The disclosed subject matter may be equallyapplicable to other video applications, including, for example, videoconferencing, digital TV broadcasting, gaming, virtual reality, storageof compressed video on digital media including CD, DVD, memory stick andthe like, and so on.

A video streaming system may include a video capture subsystem (413)that can include a video source (401), e.g., a digital camera, forcreating a stream of video pictures or images (402) that areuncompressed. In an example, the stream of video pictures (402) includessamples that are recorded by a digital camera of the video source 401.The stream of video pictures (402), depicted as a bold line to emphasizea high data volume when compared to encoded video data (404) (or codedvideo bitstreams), can be processed by an electronic device (420) thatincludes a video encoder (403) coupled to the video source (401). Thevideo encoder (403) can include hardware, software, or a combinationthereof to enable or implement aspects of the disclosed subject matteras described in more detail below. The encoded video data (404) (orencoded video bitstream (404)), depicted as a thin line to emphasize alower data volume when compared to the stream of uncompressed videopictures (402), can be stored on a streaming server (405) for future useor directly to downstream video devices (not shown). One or morestreaming client subsystems, such as client subsystems (406) and (408)in FIG. 4 can access the streaming server (405) to retrieve copies (407)and (409) of the encoded video data (404). A client subsystem (406) caninclude a video decoder (410), for example, in an electronic device(430). The video decoder (410) decodes the incoming copy (407) of theencoded video data and creates an outgoing stream of video pictures(411) that are uncompressed and that can be rendered on a display (412)(e.g., a display screen) or other rendering devices (not depicted). Thevideo decoder 410 may be configured to perform some or all of thevarious functions described in this disclosure. In some streamingsystems, the encoded video data (404), (407), and (409) (e.g., videobitstreams) can be encoded according to certain video coding/compressionstandards. Examples of those standards include ITU-T RecommendationH.265. In an example, a video coding standard under development isinformally known as Versatile Video Coding (VVC). The disclosed subjectmatter may be used in the context of VVC, and other video codingstandards.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anyembodiment of the present disclosure below. The video decoder (510) canbe included in an electronic device (530). The electronic device (530)can include a receiver (531) (e.g., receiving circuitry). The videodecoder (510) can be used in place of the video decoder (410) in theexample of FIG. 4 .

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510). In the same or another embodiment,one coded video sequence may be decoded at a time, where the decoding ofeach coded video sequence is independent from other coded videosequences. Each video sequence may be associated with multiple videoframes or images. The coded video sequence may be received from achannel (501), which may be a hardware/software link to a storage devicewhich stores the encoded video data or a streaming source whichtransmits the encoded video data. The receiver (531) may receive theencoded video data with other data such as coded audio data and/orancillary data streams, that may be forwarded to their respectiveprocessing circuitry (not depicted). The receiver (531) may separate thecoded video sequence from the other data. To combat network jitter, abuffer memory (515) may be disposed in between the receiver (531) and anentropy decoder/parser (520) (“parser (520)” henceforth). In certainapplications, the buffer memory (515) may be implemented as part of thevideo decoder (510). In other applications, it can be outside of andseparate from the video decoder (510) (not depicted). In still otherapplications, there can be a buffer memory (not depicted) outside of thevideo decoder (510) for the purpose of, for example, combating networkjitter, and there may be another additional buffer memory (515) insidethe video decoder (510), for example to handle playback timing. When thereceiver (531) is receiving data from a store/forward device ofsufficient bandwidth and controllability, or from an isosynchronousnetwork, the buffer memory (515) may not be needed, or can be small. Foruse on best-effort packet networks such as the Internet, the buffermemory (515) of sufficient size may be required, and its size can becomparatively large. Such buffer memory may be implemented with anadaptive size, and may at least partially be implemented in an operatingsystem or similar elements (not depicted) outside of the video decoder(510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such asdisplay (512) (e.g., a display screen) that may or may not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as is shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received by theparser (520). The entropy coding of the coded video sequence can be inaccordance with a video coding technology or standard, and can followvarious principles, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (520) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thesubgroups. The subgroups can include Groups of Pictures (GOPs),pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks,Transform Units (TUs), Prediction Units (PUs) and so forth. The parser(520) may also extract from the coded video sequence information such astransform coefficients (e.g., Fourier transform coefficients), quantizerparameter values, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple differentprocessing or functional units depending on the type of the coded videopicture or parts thereof (such as: inter and intra picture, inter andintra block), and other factors. The units that are involved and howthey are involved may be controlled by the subgroup control informationthat was parsed from the coded video sequence by the parser (520). Theflow of such subgroup control information between the parser (520) andthe multiple processing or functional units below is not depicted forsimplicity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these functional units interact closelywith each other and can, at least partly, be integrated with oneanother. However, for the purpose of describing the various functions ofthe disclosed subject matter with clarity, the conceptual subdivisioninto the functional units is adopted in the disclosure below.

A first unit may include the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) may receive a quantized transformcoefficient as well as control information, including informationindicating which type of inverse transform to use, block size,quantization factor/parameters, quantization scaling matrices, and thelie as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values that canbe input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block, i.e., a block that does not usepredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) may generate a block of the same size and shape ofthe block under reconstruction using surrounding block information thatis already reconstructed and stored in the current picture buffer (558).The current picture buffer (558) buffers, for example, partlyreconstructed current picture and/or fully reconstructed currentpicture. The aggregator (555), in some implementations, may add, on aper sample basis, the prediction information the intra prediction unit(552) has generated to the output sample information as provided by thescaler/inverse transform unit (551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forinter-picture prediction. After motion compensating the fetched samplesin accordance with the symbols (521) pertaining to the block, thesesamples can be added by the aggregator (555) to the output of thescaler/inverse transform unit (551) (output of unit 551 may be referredto as the residual samples or residual signal) so as to generate outputsample information. The addresses within the reference picture memory(557) from where the motion compensation prediction unit (553) fetchesprediction samples can be controlled by motion vectors, available to themotion compensation prediction unit (553) in the form of symbols (521)that can have, for example X, Y components (shift), and referencepicture components (time). Motion compensation may also includeinterpolation of sample values as fetched from the reference picturememory (557) when sub-sample exact motion vectors are in use, and mayalso be associated with motion vector prediction mechanisms, and soforth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values. Several type of loop filters may beincluded as part of the loop filter unit 556 in various orders, as willbe described in further detail below.

The output of the loop filter unit (556) can be a sample stream that canbe output to the rendering device (512) as well as stored in thereference picture memory (557) for use in future inter-pictureprediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future inter-picture prediction. For example,once a coded picture corresponding to a current picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, the parser (520)), the current picture buffer(558) can become a part of the reference picture memory (557), and afresh current picture buffer can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology adopted in a standard, suchas ITU-T Rec. H.265. The coded video sequence may conform to a syntaxspecified by the video compression technology or standard being used, inthe sense that the coded video sequence adheres to both the syntax ofthe video compression technology or standard and the profiles asdocumented in the video compression technology or standard.Specifically, a profile can select certain tools from all the toolsavailable in the video compression technology or standard as the onlytools available for use under that profile. To be standard-compliant,the complexity of the coded video sequence may be within bounds asdefined by the level of the video compression technology or standard. Insome cases, levels restrict the maximum picture size, maximum framerate, maximum reconstruction sample rate (measured in, for examplemegasamples per second), maximum reference picture size, and so on.Limits set by levels can, in some cases, be further restricted throughHypothetical Reference Decoder (HRD) specifications and metadata for HRDbuffer management signaled in the coded video sequence.

In some example embodiments, the receiver (531) may receive additional(redundant) data with the encoded video. The additional data may beincluded as part of the coded video sequence(s). The additional data maybe used by the video decoder (510) to properly decode the data and/or tomore accurately reconstruct the original video data. Additional data canbe in the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anexample embodiment of the present disclosure. The video encoder (603)may be included in an electronic device (620). The electronic device(620) may further include a transmitter (640) (e.g., transmittingcircuitry). The video encoder (603) can be used in place of the videoencoder (403) in the example of FIG. 4 .

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the example ofFIG. 6 ) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) may beimplemented as a portion of the electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 YCrCb, RGB, XYZ . . .), and any suitable sampling structure (for example YCrCb 4:2:0, YCrCb4:4:4). In a media serving system, the video source (601) may be astorage device capable of storing previously prepared video. In avideoconferencing system, the video source (601) may be a camera thatcaptures local image information as a video sequence. Video data may beprovided as a plurality of individual pictures or images that impartmotion when viewed in sequence. The pictures themselves may be organizedas a spatial array of pixels, wherein each pixel can comprise one ormore samples depending on the sampling structure, color space, and thelike being in use. A person having ordinary skill in the art can readilyunderstand the relationship between pixels and samples. The descriptionbelow focuses on samples.

According to some example embodiments, the video encoder (603) may codeand compress the pictures of the source video sequence into a codedvideo sequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speedconstitutes one function of a controller (650). In some embodiments, thecontroller (650) may be functionally coupled to and control otherfunctional units as described below. The coupling is not depicted forsimplicity. Parameters set by the controller (650) can include ratecontrol related parameters (picture skip, quantizer, lambda value ofrate-distortion optimization techniques, . . . ), picture size, group ofpictures (GOP) layout, maximum motion vector search range, and the like.The controller (650) can be configured to have other suitable functionsthat pertain to the video encoder (603) optimized for a certain systemdesign.

In some example embodiments, the video encoder (603) may be configuredto operate in a coding loop. As an oversimplified description, in anexample, the coding loop can include a source coder (630) (e.g.,responsible for creating symbols, such as a symbol stream, based on aninput picture to be coded, and a reference picture(s)), and a (local)decoder (633) embedded in the video encoder (603). The decoder (633)reconstructs the symbols to create the sample data in a similar manneras a (remote) decoder would create even though the embedded decoder 633process coded video steam by the source coder 630 without entropy coding(as any compression between symbols and coded video bitstream in entropycoding may be lossless in the video compression technologies consideredin the disclosed subject matter). The reconstructed sample stream(sample data) is input to the reference picture memory (634). As thedecoding of a symbol stream leads to bit-exact results independent ofdecoder location (local or remote), the content in the reference picturememory (634) is also bit exact between the local encoder and remoteencoder. In other words, the prediction part of an encoder “sees” asreference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used to improve coding quality.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633) inthe encoder.

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that may only be presentin a decoder also may necessarily need to be present, in substantiallyidentical functional form, in a corresponding encoder. For this reason,the disclosed subject matter may at times focus on decoder operation,which allies to the decoding portion of the encoder. The description ofencoder technologies can thus be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas or aspects a more detail description of the encoder is providedbelow.

During operation in some example implementations, the source coder (630)may perform motion compensated predictive coding, which codes an inputpicture predictively with reference to one or more previously codedpicture from the video sequence that were designated as “referencepictures.” In this manner, the coding engine (632) codes differences (orresidue) in the color channels between pixel blocks of an input pictureand pixel blocks of reference picture(s) that may be selected asprediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end (remote) video decoder (absent transmissionerrors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compression of the symbols accordingto technologies such as Huffman coding, variable length coding,arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person having ordinary skill in the art is aware of thosevariants of I pictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample coding blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16samples each) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures. The sourcepictures or the intermediate processed pictures may be subdivided intoother types of blocks for other purposes. The division of coding blocksand the other types of blocks may or may not follow the same manner, asdescribed in further detail below.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data may accordingly conform to a syntax specified bythe video coding technology or standard being used.

In some example embodiments, the transmitter (640) may transmitadditional data with the encoded video. The source coder (630) mayinclude such data as part of the coded video sequence. The additionaldata may comprise temporal/spatial/SNR enhancement layers, other formsof redundant data such as redundant pictures and slices, SEI messages,VUI parameter set fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) utilizes spatial correlation in a givenpicture, and inter-picture prediction utilizes temporal or othercorrelation between the pictures. For example, a specific picture underencoding/decoding, which is referred to as a current picture, may bepartitioned into blocks. A block in the current picture, when similar toa reference block in a previously coded and still buffered referencepicture in the video, may be coded by a vector that is referred to as amotion vector. The motion vector points to the reference block in thereference picture, and can have a third dimension identifying thereference picture, in case multiple reference pictures are in use.

In some example embodiments, a bi-prediction technique can be used forinter-picture prediction. According to such bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that both proceed the current picture in the video indecoding order (but may be in the past or future, respectively, indisplay order) are used. A block in the current picture can be coded bya first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bejointly predicted by a combination of the first reference block and thesecond reference block.

Further, a merge mode technique may be used in the inter-pictureprediction to improve coding efficiency.

According to some example embodiments of the disclosure, predictions,such as inter-picture predictions and intra-picture predictions areperformed in the unit of blocks. For example, a picture in a sequence ofvideo pictures is partitioned into coding tree units (CTU) forcompression, the CTUs in a picture may have the same size, such as 64×64pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may includethree parallel coding tree blocks (CTBs): one luma CTB and two chromaCTBs. Each CTU can be recursively quadtree split into one or multiplecoding units (CUs). For example, a CTU of 64×64 pixels can be split intoone CU of 64×64 pixels, or 4 CUs of 32×32 pixels. Each of the one ormore of the 32×32 block may be further split into 4 CUs of 16×16 pixels.In some example embodiments, each CU may be analyzed during encoding todetermine a prediction type for the CU among various prediction typessuch as an inter prediction type or an intra prediction type. The CU maybe split into one or more prediction units (PUs) depending on thetemporal and/or spatial predictability. Generally, each PU includes aluma prediction block (PB), and two chroma PBs. In an embodiment, aprediction operation in coding (encoding/decoding) is performed in theunit of a prediction block. The split of a CU into PU (or PBs ofdifferent color channels) may be performed in various spatial pattern. Aluma or chroma PB, for example, may include a matrix of values (e.g.,luma values) for samples, such as 8×8 pixels, 16×16 pixels, 8×16 pixels,16×8 samples, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherexample embodiment of the disclosure. The video encoder (703) isconfigured to receive a processing block (e.g., a prediction block) ofsample values within a current video picture in a sequence of videopictures, and encode the processing block into a coded picture that ispart of a coded video sequence. The example video encoder (703) may beused in place of the video encoder (403) in the FIG. 4 example.

For example, the video encoder (703) receives a matrix of sample valuesfor a processing block, such as a prediction block of 8×8 samples, andthe like. The video encoder (703) then determines whether the processingblock is best coded using intra mode, inter mode, or bi-prediction modeusing, for example, rate-distortion optimization (RDO). When theprocessing block is determined to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis determined to be coded in inter mode or bi-prediction mode, the videoencoder (703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Insome example embodiments, a merge mode may be used as a submode of theinter picture prediction where the motion vector is derived from one ormore motion vector predictors without the benefit of a coded motionvector component outside the predictors. In some other exampleembodiments, a motion vector component applicable to the subject blockmay be present. Accordingly, the video encoder (703) may includecomponents not explicitly shown in FIG. 7 , such as a mode decisionmodule, to determine the perdition mode of the processing blocks.

In the example of FIG. 7 , the video encoder (703) includes an interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in the examplearrangement in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures in display order), generate inter predictioninformation (e.g., description of redundant information according tointer encoding technique, motion vectors, merge mode information), andcalculate inter prediction results (e.g., predicted block) based on theinter prediction information using any suitable technique. In someexamples, the reference pictures are decoded reference pictures that aredecoded based on the encoded video information using the decoding unit633 embedded in the example encoder 620 of FIG. 6 (shown as residualdecoder 728 of FIG. 7 , as described in further detail below).

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to blocksalready coded in the same picture, and generate quantized coefficientsafter transform, and in some cases also to generate intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). The intra encoder (722) maycalculates intra prediction results (e.g., predicted block) based on theintra prediction information and reference blocks in the same picture.

The general controller (721) may be configured to determine generalcontrol data and control other components of the video encoder (703)based on the general control data. In an example, the general controller(721) determines the prediction mode of the block, and provides acontrol signal to the switch (726) based on the prediction mode. Forexample, when the prediction mode is the intra mode, the generalcontroller (721) controls the switch (726) to select the intra moderesult for use by the residue calculator (723), and controls the entropyencoder (725) to select the intra prediction information and include theintra prediction information in the bitstream; and when the predicationmode for the block is the inter mode, the general controller (721)controls the switch (726) to select the inter prediction result for useby the residue calculator (723), and controls the entropy encoder (725)to select the inter prediction information and include the interprediction information in the bitstream.

The residue calculator (723) may be configured to calculate a difference(residue data) between the received block and prediction results for theblock selected from the intra encoder (722) or the inter encoder (730).The residue encoder (724) may be configured to encode the residue datato generate transform coefficients. For example, the residue encoder(724) may be configured to convert the residue data from a spatialdomain to a frequency domain to generate the transform coefficients. Thetransform coefficients are then subject to quantization processing toobtain quantized transform coefficients. In various example embodiments,the video encoder (703) also includes a residue decoder (728). Theresidue decoder (728) is configured to perform inverse-transform, andgenerate the decoded residue data. The decoded residue data can besuitably used by the intra encoder (722) and the inter encoder (730).For example, the inter encoder (730) can generate decoded blocks basedon the decoded residue data and inter prediction information, and theintra encoder (722) can generate decoded blocks based on the decodedresidue data and the intra prediction information. The decoded blocksare suitably processed to generate decoded pictures and the decodedpictures can be buffered in a memory circuit (not shown) and used asreference pictures.

The entropy encoder (725) may be configured to format the bitstream toinclude the encoded block and perform entropy coding. The entropyencoder (725) is configured to include in the bitstream variousinformation. For example, the entropy encoder (725) may be configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. When coding a block in the merge submode of either inter modeor bi-prediction mode, there may be no residue information.

FIG. 8 shows a diagram of an example video decoder (810) according toanother embodiment of the disclosure. The video decoder (810) isconfigured to receive coded pictures that are part of a coded videosequence, and decode the coded pictures to generate reconstructedpictures. In an example, the video decoder (810) may be used in place ofthe video decoder (410) in the example of FIG. 4 .

In the example of FIG. 8 , the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in the example arrangement of FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (e.g., intra mode, intermode, bi-predicted mode, merge submode or another submode), predictioninformation (e.g., intra prediction information or inter predictioninformation) that can identify certain sample or metadata used forprediction by the intra decoder (872) or the inter decoder (880),residual information in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isthe inter or bi-predicted mode, the inter prediction information isprovided to the inter decoder (880); and when the prediction type is theintra prediction type, the intra prediction information is provided tothe intra decoder (872). The residual information can be subject toinverse quantization and is provided to the residue decoder (873).

The inter decoder (880) may be configured to receive the interprediction information, and generate inter prediction results based onthe inter prediction information.

The intra decoder (872) may be configured to receive the intraprediction information, and generate prediction results based on theintra prediction information.

The residue decoder (873) may be configured to perform inversequantization to extract de-quantized transform coefficients, and processthe de-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso utilize certain control information (to include the QuantizerParameter (QP)) which may be provided by the entropy decoder (871) (datapath not depicted as this may be low data volume control informationonly).

The reconstruction module (874) may be configured to combine, in thespatial domain, the residual as output by the residue decoder (873) andthe prediction results (as output by the inter or intra predictionmodules as the case may be) to form a reconstructed block forming partof the reconstructed picture as part of the reconstructed video. It isnoted that other suitable operations, such as a deblocking operation andthe like, may also be performed to improve the visual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In some example embodiments, the video encoders(403), (603), and (703), and the video decoders (410), (510), and (810)can be implemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Returning to the intra prediction process, in which samples in a block(e.g., a luma or chroma prediction block, or coding block if not furthersplit into prediction blocks) is predicted by samples of neighboring,next neighboring, or other line or lines, or the combination thereof, togenerate a prediction block. The residual between the actual block beingcoded and the prediction block may then be processed via transformfollowed by quantization. Various intra prediction modes may be madeavailable and parameters related to intra mode selection and otherparameters may be signaled in the bitstream. The various intraprediction modes, for example, may pertain to line position or positionsfor predicting samples, directions along which prediction samples areselected from predicting line or lines, and other special intraprediction modes.

For example, a set of intra prediction modes (interchangeably referredto as “intra modes”) may include a predefined number of directionalintra prediction modes. As described above in relation to the exampleimplementation of FIG. 1 , these intra prediction modes may correspondto a predefined number of directions along which out-of-block samplesare selected as prediction for samples being predicted in a particularblock. In another particular example implementation, eight (8) maindirectional modes corresponding to angles from 45 to 207 degrees to thehorizontal axis may be supported and predefined.

In some other implementations of intra prediction, to further exploitmore varieties of spatial redundancy in directional textures,directional intra modes may be further extended to an angle set withfiner granularity. For example, the 8-angle implementation above may beconfigured to provide eight nominal angles, referred to as V_PRED,H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, andD67_PRED, as illustrated in FIG. 9 , and for each nominal angle, apredefined number (e.g., 7) of finer angles may be added. With such anextension, a larger total number (e.g., 56 in this example) ofdirectional angles may be available for intra prediction, correspondingto the same number of predefined directional intra modes. A predictionangle may be represented by a nominal intra angle plus an angle delta.For the particular example above with 7 finer angular directions foreach nominal angle, the angle delta may be −3˜3 multiplies a step sizeof 3 degrees.

The above directional intra prediction may also be referred as singledirectional intra prediction, which is different from bi-directionalintra prediction (also referred as intra bi-prediction) described inlater part of the present disclosure.

In some implementations, alternative or in addition to the directionintra modes above, a predefined number of non-directional intraprediction modes may also be predefined and made available. For example,5 non-direction intra modes referred to as smooth intra prediction modesmay be specified. These non-directional intra mode prediction modes maybe specifically referred to as DC, PAETH, SMOOTH, SMOOTH_V, and SMOOTH_Hintra modes. Prediction of samples of a particular block under theseexample non-directional modes are illustrated in FIG. 10 . As anexample, FIG. 10 shows a 4×4 block 1002 being predicted by samples froma top neighboring line and/or left neighboring line. A particular sample1010 in block 1002 may correspond to directly top sample 1004 of thesample 1010 in the top neighboring line of block 1002, a top-left sample1006 of the sample 1010 as the intersection of the top and leftneighboring lines, and a directly left sample 1008 of the sample 1010 inthe left neighboring line of block 1002. For the example DC intraprediction mode, an average of the left and above neighboring samples1008 and 1004 may be used as the predictor of the sample 1010. For theexample PAETH intra prediction mode, the top, left, and top-leftreference samples 1004, 1008, and 1006 may be fetched, and thenwhichever value among these three reference samples that is the closestto (top+left−topleft) may be set as the predictor for the sample 1010.For the example SMOOTH_V intra prediction mode, the sample 1010 may bepredicted by a quadratic interpolation in vertical direction of thetop-left neighboring sample 1006 and the left neighboring sample 1008.For the example SMOOTH_H intra prediction mode, the sample 1010 may bepredicted by a quadratic interpolation in horizontal direction of thetop-left neighboring sample 1006 and the top neighboring sample 1004.For the example SMOOTH intra prediction mode, the sample 1010 may bepredicted by an average of the quadratic interpolations in the verticaland the horizontal directions. The non-directional intra modeimplementations above are merely illustrated as a non-limiting example.Other neighboring lines, and other non-directional selection of samples,and manners of combining predicting samples for predicting a particularsample in a prediction block are also contemplated.

Selection of a particular intra prediction mode by the encoder from thedirectional or non-directional modes above at various coding levels(picture, slice, block, unit, etc.) may be signaled in the bitstream. Insome example implementations, the exemplary 8 nominal directional modestogether with 5 non-angular smooth modes (a total of 13 options) may besignaled first. Then if the signaled mode is one of the 8 nominalangular intra modes, an index is further signaled to indicate theselected angle delta to the corresponding signaled nominal angle. Insome other example implementations, all intra prediction modes may beindexed all together (e.g., 56 directional modes plus 5 non-directionalmodes to yield 61 intra prediction modes) for signaling.

In some example implementations, the example 56 or other number ofdirectional intra prediction modes may be implemented with a unifieddirectional predictor that projects each sample of a block to areference sub-sample location and interpolates the reference sample by a2-tap bilinear filter.

In some implementations, to capture decaying spatial correlation withreferences on the edges, additional filter modes referred to as FILTERINTRA modes may be designed. For these modes, predicted samples withinthe block in addition to out-of-block samples may be used as intraprediction reference samples for some patches within the block. Thesemodes, for example, may be predefined and made available to intraprediction for at least luma blocks (or only luma blocks). A predefinednumber (e.g., five) of filter intra modes may be pre-designed, eachrepresented by a set of n-tap filters (e.g., 7-tap filters) reflectingcorrelation between samples in, for example, a 4×2 patch and n neighborsadjacent to it. In other words, the weighting factors for an n-tapfilter may be position dependent. Taking an 8×8 block, 4×2 patch, and7-tap filtering as an example, as shown in FIG. 11 , the 8×8 block 1102may be split into eight 4×2 patches. These patches are indicated by B0,B1, B1, B3, B4, B5, B6, and B7 in FIG. 11 . For each patch, its 7neighbors, indicated by R0˜R7 in FIG. 11 , may be used to predict thesamples in a current patch. For patch B0, all the neighbors may havebeen already reconstructed. But for other patches, some of the neighborsare in the current block and thus may not have been reconstructed, thenthe predicted values of immediate neighbors are used as the reference.For example, all the neighbors of patch B7 as indicated in FIG. 11 arenot reconstructed, so the prediction samples of neighbors, for example aportion of B4, B5, and/or B6, are used instead.

In some implementation of intra prediction, one color component may bepredicted using one or more other color components. A color componentmay be any one of components in YCrCb, RGB, XYZ color space and thelike. For example, a prediction of chroma component (e.g., chroma block)from luma component (e.g., luma reference samples), referred to asChroma from Luma, or CfL), may be implemented. In some exampleimplementations, cross-color prediction many only be allowed from lumato chroma. For example, a chroma sample in a chroma block may be modeledas a linear function of coincident reconstructed luma samples. The CfLprediction may be implemented as follows:

CfL(α)=α×L ^(AC) +DC  (1)

where L^(AC) denotes an AC contribution of luma component, a denotes aparameter of the linear model, and DC denotes a DC contribution of thechroma component. The AC components, for example is obtained for eachsamples of the block whereas the DC component is obtained for the entireblock. To be specific, the reconstructed luma samples may be subsampledinto the chroma resolution, and then the average luma value (DC of luma)may be subtracted from each luma value to form the AC contribution inluma. The AC contribution of Luma is then used in the linear mode of Eq.(1) to predict the AC values of the chroma component. To approximate orpredict chroma AC component from the luma AC contribution, instead ofrequiring the decoder to calculate the scaling parameters, an exampleCfL implementation may determine the parameter a based on the originalchroma samples and signal them in the bitstream. This reduces decodercomplexity and yields more precise predictions. As for the DCcontribution of the chroma component, it may be computed using intra DCmode within the chroma component in some example implementations.

Turning back to intra prediction, in some example implementations,prediction of samples in a coding block or prediction block may be basedon one of a set of reference lines. In other words, rather than alwaysusing a nearest neighboring line (e.g., the immediate top neighboringline or the immediate left neighboring line of the prediction block asillustrated in FIG. 1 above), multiple reference lines may be providedas options for selection for intra prediction. Such intra predictionimplementations may be referred to as Multiple Reference Line Selection(MRLS). In these implementations, an encoder decides and signals whichreference line of a plurality of reference lines is used to generate theintra predictor. At the decoder side, after parsing the reference lineindex, the intra prediction of current intra-prediction block can begenerated by identifying the reconstructed reference samples by lookingup the specified reference line according to the intra prediction mode(such the directional, non-directional, and other intra-predictionmodes). In some implementations, a reference line index may be signaledin the coding block level and only one of the multiple reference linesmay be selected and used for intra prediction of one coding block. Insome examples, more than one reference lines may be selected togetherfor intra-prediction. For example, the more than one reference lines maybe combined, averaged, interpolated or in any other manner, with orwithout weight, to generate the prediction. In some exampleimplementations, MRLS may only be applied to luma component and may notbe applied to chroma component(s).

In FIG. 12 , an example of 4 reference-line MRLS is depicted. As shownin the example of FIG. 12 , the intra-coding block 1202 may be predictedbased on one of the 4 horizontal reference lines 1204, 1206, 1208, and1210 and 4 vertical reference lines 1212, 1214, 1216, and 1218. Amongthese reference lines, 1210 and 1218 are the immediate neighboringreference lines. The reference lines may be indexed according to theirdistance from the coding block. For example, reference lines 1210 and1218 may be referred to as zero reference line whereas the otherreference lines may be referred to as non-zero reference lines.Specifically, reference lines 1208 and 1216 may be reference as 1^(st)reference lines; reference lines 1206 and 1214 may be reference as 2ndreference lines; and reference lines 1204 and 1212 may be reference as3rd reference lines.

In addition to the single directional intra prediction described in theearlier part of the present disclosure, two reference pixels along aprediction direction may be used in a combination manner to achieve thedirectional predictor, which may be referred as bi-directional intraprediction, or intra bi-prediction (IBP).

In some implementations, for a current block (e.g., a coding block or acoded block), IBP may be applicable to a directional mode when thedirection mode has an angle smaller than 90 degree, for example but notlimited to, the D67_PRED and D45_PRED in FIG. 9 . In some otherimplementation, IBP may be also applicable to a directional mode whenthe direction mode has an angle larger than 180 degree, for example butnot limited to, the D203_PRED in FIG. 9 .

When intra bi-prediction is applied, two reference pixels along thedirection of the direction mode are selected: one reference pixel isfrom a top or top right of the current block, and the other pixel isfrom a left or lower left of the current block. a weighted average ofthe two reference pixels may be calculated to achieve the predictor.

FIG. 13A shows an example of IBP for a coded block (1330) with adirection mode having a prediction direction (1340) from A (1322) to B(1312). A and B are two reference samples/values, which are alsoreferred as a first predictor and a second predictor. A is at a cross ofthe direction (1340) and a top reference line (1320); and B is at across of the direction (1340) and a left reference line (1310). Theprediction for a pixel (x,y) (1332), which is a pixel in the coded block(1330), is denoted as pred(x,y). pred(x,y) may be generated with theweighted combination of the two predictors A and B, as shown in Eq. (2).

Pred(x,y)=w*A+(1−w)*B  (2)

A and/or B may be derived with a directional prediction process whichincludes interpolation for fractional-pixel reference. FIG. 13B showsanother example of IBP for the coded block (1330) with a differentdirection mode having a different prediction direction (1350) from A(1314) to B (1324).

In some implementations wherein IBP is applied, two reference pixelslocated at the adjacent above reference line and adjacent left referencealong the direction are weighted to achieve the predictor. Both IBP andmultiple reference line selection (MRLS) may be applied to a codedblock, resulting in some issues/problems. For example, one issue/problemmay include how to apply IBP to the current block when one or morereference samples in one or more non-adjacent reference lines areselected.

The present disclosure describes various embodiment for signaling and/ordetermining multiple reference line intra prediction in video codingand/or decoding, addressing at least one of the issues/problemsdiscussed above.

In various embodiment, referring to FIG. 14 , a method 1400 for intrabi-prediction and multiple reference line intra prediction in videodecoding. The method 1400 may include a portion or all of the followingsteps: step 1410, receiving, by a device comprising a memory storinginstructions and a processor in communication with the memory, a codedvideo bitstream for a block; step 1420, determining, by the device,whether a single directional intra prediction or an intra bi-predictionapplies to the block based on mode information of the block, the modeinformation of the block comprising at least one of a reference lineindex of the block, an intra prediction mode of the block, and a size ofthe block; step 1430, in response to determining that the singledirectional intra prediction applies to the block, performing, by thedevice, the single directional intra prediction to the block; and/orstep 1440, in response to determining that the intra bi-predictionapplies to the block, performing, by the device, the intra bi-predictionto the block. In some implementations, step 1420 may includedetermining, by the device, whether single directional intra predictionor intra bi-prediction applies to the block, based on mode informationof the block, the mode information of the block comprising at least oneof the following: a reference line index of the block, an intraprediction mode of the block, or a size of the block.

In some implementations, when an intra prediction mode does not belongto one of the smooth modes as discussed above or when an intraprediction mode generates one or more prediction sample according to agiven prediction direction, this intra prediction mode may becategorized as one of directional modes, and/or this intra predictionmode may be referred as a directional intra prediction mode (ordirectional mode).

In various embodiments in the present disclosure, a size of a block (forexample but not limited to, a coding block, a prediction block, or atransform block) may refer to a width or a height of the block. Thewidth or the height of the block may be an integer in a unit of pixels.

In various embodiments in the present disclosure, a size of a block (forexample but not limited to, a coding block, a prediction block, or atransform block) may refer to an area size of the block. The area sizeof the block may be an integer calculated by the width of the blockmultiplied by the height of the bock in a unit of pixels.

In some various embodiments in the present disclosure, a size of a block(for example but not limited to, a coding block, a prediction block, ora transform block) may refer to a maximum value of a width or a heightof the block, a minimum value of a width or a height of the block, or anaspect ratio of the block. The aspect ratio of the block may becalculated as the width divided by the height of the block, or may becalculated as the height divided by the width of the block.

In the present disclosure, a reference line index indicates a referenceline among multiple reference lines. In various embodiments, thereference line index being 0 for a block may indicate the adjacentreference line to the block, which is also the nearest reference line tothe block. For example, referring to a block (1202) in FIG. 12 , a topreference line (1210) is a top adjacent reference line to the block(1202), which is also a top nearest reference line to the block; and aleft reference line (1218) is a left adjacent reference line to theblock (1202), which is also a left nearest reference line to the block.A reference line index being greater than 0 for a block indicates anon-adjacent reference line of the block, which is also the non-nearestreference line to the block. For example, referring to a block (1202) inFIG. 12 , a reference line index being 1 may indicate a top referenceline (1208) and/or a left reference line (1216); a reference line indexbeing 2 may indicate a top reference line (1206) and/or a left referenceline (1214); and/or a reference line index being 3 may indicate a topreference line (1204) and/or a left reference line (1212).

Referring to step 1410, the device may be the electronic device (530) inFIG. 5 or the video decoder (810) in FIG. 8 . In some implementations,the device may be the decoder (633) in the encoder (620) in FIG. 6 . Inother implementations, the device may be a portion of the electronicdevice (530) in FIG. 5 , a portion of the video decoder (810) in FIG. 8, or a portion of the decoder (633) in the encoder (620) in FIG. 6 . Thecoded video bitstream may be the coded video sequence in FIG. 8 , or anintermediate coded data in FIG. 6 or 7 . The block may refer to a codingblock or a coded block.

In some implementations, when a directional intra prediction mode isselected for a block to generate an intra predictor from samples at thenon-adjacent reference lines, whether a single directional intraprediction or an intra bi-prediction is applied to the block may bedetermined, and this determination may depend on mode information of theblock. In some implementations, the mode information of the block mayinclude but not limited to, a reference line index (e.g., indicatingwhich reference line among multiple reference lines), one or more intraprediction angles (e.g., indicating which directional intra predictionmode among multiple directional intra predication modes), and/or a sizeof the block.

Referring to step 1420, the device may determine whether singledirectional intra prediction or intra bi-prediction applies to theblock, based on the mode information of the block. In someimplementations, step 1420 may include, in response to the referenceline index of the block indicating a non-adjacent reference line,determining that the single directional intra prediction applies to theblock. As one example, a single directional intra prediction may beapplied to non-adjacent reference lines regardless of the intraprediction angles of a current block.

In various embodiments, step 1420 may include, in response to thereference line index of the block indicating an adjacent reference line,determining that the intra bi-prediction applies to the block. As oneexample, an intra bi-prediction may only be applied to an adjacentreference line for a current block.

In various embodiments, step 1420 may include, in response to thereference line index of the block being greater than a predefinedthreshold, determining that the single directional intra predictionapplies to the block; and/or in response to the reference line index ofthe block not being greater than the predefined threshold, determiningthat the intra bi-prediction applies to the block. As one example, thedetermination on whether single directional intra prediction or intrabi-prediction is applied to non-adjacent reference lines, and thisdetermination also depends on whether the value of reference line indexis greater than a predefined value N. N is a non-negative integer, forexample 0, 1, 2, 3, or 4.

In one example, the predefined value N is 0. The single directionalintra prediction applies to the block when the value of reference lineindex for the block is greater than 0, i.e., when any non-adjacentreference line (e.g., any line of 1212, 1214, 1216, 1204, 1206, and/or1208 in FIG. 12 ) is used for the block; and/or the intra bi-predictionapplies to the block when the value of reference line index for theblock is not greater than 0, i.e., when an adjacent reference line(e.g., any line of 1218 and/or 1210 in FIG. 12 ) is used for the block.

In another example, the predefined value N is 1. The single directionalintra prediction applies to the block when the value of reference lineindex for the block is greater than 1, i.e., when any of a first subsetof non-adjacent reference lines (e.g., any line of 1212, 1214, 1204,and/or 1206 in FIG. 12 ) is used for the block; and/or the intrabi-prediction applies to the block when the value of reference lineindex for the block is not greater than 1, i.e., when an adjacentreference line (e.g., any line of 1218 and/or 1210 in FIG. 12 ) and/orany of a second subset of non-adjacent reference lines (e.g., any lineof 1208 and/or 1216 in FIG. 12 ) is used for the block.

In various embodiments, step 1420 may include, in response to the intraprediction mode of the block belonging to a first selected set of intraprediction modes and the reference line index indicating an adjacentreference line, determining that the intra bi-prediction applies to theblock; in response to the intra prediction mode of the block belongingto the first selected set of intra prediction modes and the referenceline index indicating a non-adjacent reference line, determining thatthe single directional intra prediction applies to the block; and/or inresponse to the intra prediction mode of the block belonging to a secondselected set of intra prediction modes, determining that the intrabi-prediction applies to the block. In some implementations, the firstselected set of intra prediction modes does not overlap with the secondselected set of intra prediction modes. In some other implementations,the second selected set of intra prediction modes may include a diagonalintra prediction mode.

In some implementations, for a selected set of intra prediction modes,IBP is applied for both adjacent and non-adjacent reference lines, whilefor the remaining set of intra prediction modes, IBP is only applied foradjacent reference lines. In some other implementations, the selectedset of intra prediction modes may include several intra prediction modeswith some specific direction angles, so that only integer samples areused as reference values for intra prediction. For one example, onlyinteger samples are used as reference values for some intra predictionmodes having a diagonal direction (i.e., 45 degrees or 225 degrees). Foranother example, when the intra prediction is applied by only usinginteger samples for diagonal intra prediction modes, IBP may be appliedfor non-adjacent reference lines as well, wherein the diagonal intraprediction mode is a intra prediction mode having a diagonal direction(i.e., 45 degrees or 225 degrees).

In various embodiments, step 1420 may include, in response to thereference line index of the block being an odd integer and/or thereference line index indicating a non-adjacent reference line,determining that the single directional intra prediction applies to theblock; and/or in response to the reference line index of the block beingan even integer and/or the reference line index indicating an adjacentreference line, determining that the intra bi-prediction applies to theblock.

In some implementations, the determination on whether single directionalintra prediction or intra bi-prediction is applied to non-adjacentreference lines, and the determination depends on whether a value ofreference line index is an even number or an odd number. For oneexample, when the value of reference line index for a block is an oddnumber, a single directional intra prediction is applied to the block;and/or when the value of reference line index for the block is an evennumber, an intra bi-prediction is applied to the block. For anotherexample, when the value of reference line index for a block is an evennumber, a single directional intra prediction is applied to the block;and/or when the value of reference line index for the block is an oddnumber, an intra bi-prediction is applied to the block.

In various embodiments, there may be only one reference line index for ablock. During encoding, the reference line index for the block may beencoded into the coded bitstream; and/or during decoding, the referenceline index for the block may be decoded/extracted from the codedbitstream. The step 1440 may include, determining a first predictorbased on the reference line index of the block; determining a secondpredictor based on the reference line index of the block; and/ordetermining a final predictor for the block according to a weightedcalculation between the first predictor and the second predictor.

In some implementations, when intra bi-prediction is applied and thereference line index for the block indicating to use non-adjacentreference lines for intra prediction, to generate the intra predictorfrom samples at the non-adjacent reference lines, both predictor A andpredictor B are generated from the samples at non-adjacent referencelines, and then a weighted calculation is performed based on predictor Aand predictor B to generate the final IBP predictor.

In various embodiments, there may be more than one reference lineindexes for a block. A first reference line index may indicate areference line to use among multiple top reference lines and a secondreference line index may indicate a reference line to use among multipleleft reference lines; or vice versa, a first reference line index mayindicate a reference line to use among multiple left reference lines anda second reference line index may indicate a reference line to use amongmultiple top reference lines. During encoding, the more than onereference line indexes for the block may be encoded into the codedbitstream; and/or during decoding, the more than one reference lineindexes for the block may be decoded/extracted from the coded bitstream.

In some implementations, the step 1440 may include, determining a firstpredictor based on a first reference line index of the block;determining a second predictor based on a second reference line index ofthe block; and/or determining a final predictor for the block accordingto a weighted calculation between the first predictor and the secondpredictor.

In some other implementations, the first reference line index indicatesa non-adjacent reference line, and the first predictor is generated froma first sample at the non-adjacent reference line; and/or the secondreference line index indicates an adjacent reference line, and thesecond predictor is generated from a second sample at the adjacentreference line.

In one example referring to FIG. 15 , when intra bi-prediction isapplied to a coded block (1530), to generate an intra predictor (1532)from samples at two reference lines including one non-adjacent referenceline and/or one or more adjacent reference line. As shown in FIG. 15 ,the coded block has a left adjacent reference line (1510), a topadjacent reference line (1520), and at least one top adjacent referenceline (1521 and/or 1522). For example but without limitation, a firstreference line index being 2 may indicate the top non-adjacent referenceline (1522), so that Predictor A (1528) is generated from the samples atthe non-adjacent reference line (1522) selected by MRLS according to theprediction direction (1550). In some implementation, a second referenceline index being 0 may indicate the left adjacent reference line (1510).In some other implementations, the left adjacent reference line (1510)may be indicated/implied without the second reference line index.Predictor B (1514) is generated from the samples at the adjacentreference line (1510) according to the prediction direction (1550). Thenpredictor A and predictor B is weighted combined to generate the intrapredictor (1532) following the IBP scheme, for example, following theformula in Eq. (2). In some implementations, the weight (w) may dependon the distance between the intra predictor (1532) and either PredictorA or Predictor B. In Eq. (2), the smaller the distance between the intrapredictor (1532) and Predictor A (1528) (i.e., the closer the predictor(1532) to Predictor A (1528)), the bigger the weight (w) is. Similarly,in Eq. (2), the larger the distance between the intra predictor (1532)and Predictor A (1528) (i.e., the further the predictor (1532) toPredictor A (1528)), the smaller the weight (w) is.

FIG. 15 illustrates an example with a single left reference line andmultiple top reference lines; and similarly, in another example, asingle top reference line and multiple left reference lines may beapplied to a coded block when intra bi-predication is applied to thecoded block.

In various embodiments, there may be more than one reference lineindexes for a block. A first reference line index may indicate areference line to use among multiple top reference lines and a secondreference line index may indicate more than one reference lines to useamong multiple left reference lines; or vice versa, a first referenceline index may indicate a reference line to use among multiple leftreference lines and a second reference line index may indicate more thanone reference line to use among multiple top reference lines. Duringencoding, the more than one reference line indexes for the block may beencoded into the coded bitstream; and/or during decoding, the more thanone reference line indexes for the block may be decoded/extracted fromthe coded bitstream.

In some implementations, the step 1440 may include, the first referenceline index indicates a non-adjacent reference line, and the firstpredictor is generated from a first sample at the non-adjacent referenceline; and/or the second reference line index indicates a plurality ofreference lines, and the second predictor is generated as a linearweighted average of samples, each of which is from each of the pluralityof reference lines along a prediction angle.

In some other implementations, when intra bi-prediction is applied togenerate the intra predictor from samples at the non-adjacent referencelines, one or both predictors are generated using the samples atmultiple (more than 1) reference lines.

In one example referring to FIG. 16 , a predictor is generated using alinear weighted sum of more than one samples from multiple referencelines along a prediction angle (1650): a first sample (1626) from afirst reference line (1620), a second sample (1627) from a secondreference line (1621), a third sample (1628) from a third reference line(1622). Weights for each sample may be predefined according to therelative positions of the samples (of multiple reference lines) involvedin the derivation of the predictor.

In various embodiments, the method 1400 may further include: in responseto determining that the intra bi-prediction applies to the block and thereference line index of the block indicating a non-adjacent referenceline: disabling a reference sample filtering process, in response to areference sample from the non-adjacent reference being available, usingthe reference sample for intra bi-prediction, and/or in response to thereference sample from the non-adjacent reference being unavailable,using a neighboring available reference sample for intra bi-prediction.

In some implementations, a reference sample filtering process may bedisabled when bi-intra prediction is applied to one or more non-adjacentreference lines. Therefore, one or more reference samples from one ormore non-adjacent (or non-zero) reference lines may be fetched anddirectly used for intra bi-prediction. If the one or more referencesamples from the one or more non-adjacent (or non-zero) reference linesare not available, they may be padded from one or more neighboringavailable reference samples. In some other implementation, the paddingto the non-available reference sample may include copying from theneighboring available reference samples.

Embodiments in the disclosure may be used separately or combined in anyorder. Further, each of the methods (or embodiments), an encoder, and adecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium. Embodiments in the disclosure may be appliedto a luma block or a chroma block; and in the chroma block, theembodiments may be applied to more than one color components separatelyor may be applied to more than one color components together.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 17 shows a computersystem (2600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 17 for computer system (2600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2600).

Computer system (2600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2601), mouse (2602), trackpad (2603), touchscreen (2610), data-glove (not shown), joystick (2605), microphone(2606), scanner (2607), camera (2608).

Computer system (2600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2610), data-glove (not shown), or joystick (2605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2609), headphones(not depicted)), visual output devices (such as screens (2610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2620) with CD/DVD or the like media (2621), thumb-drive (2622),removable hard drive or solid state drive (2623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2600) can also include an interface (2654) to one ormore communication networks (2655). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CAN bus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general-purpose data ports or peripheral buses (2649) (such as,for example USB ports of the computer system (2600)); others arecommonly integrated into the core of the computer system (2600) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (2600) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2640) of thecomputer system (2600).

The core (2640) can include one or more Central Processing Units (CPU)(2641), Graphics Processing Units (GPU) (2642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2643), hardware accelerators for certain tasks (2644), graphicsadapters (2650), and so forth. These devices, along with Read-onlymemory (ROM) (2645), Random-access memory (2646), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(2647), may be connected through a system bus (2648). In some computersystems, the system bus (2648) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (2648), or through a peripheral bus (2649). In anexample, the screen (2610) can be connected to the graphics adapter(2650). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (2641), GPUs (2642), FPGAs (2643), and accelerators (2644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2645) or RAM (2646). Transitional data can also be stored in RAM(2646), whereas permanent data can be stored for example, in theinternal mass storage (2647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2641), GPU (2642), massstorage (2647), ROM (2645), RAM (2646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As a non-limiting example, the computer system having architecture(2600), and specifically the core (2640) can provide functionality as aresult of processor(s) (including CPUs, GPUs, FPGA, accelerators, andthe like) executing software embodied in one or more tangible,computer-readable media. Such computer-readable media can be mediaassociated with user-accessible mass storage as introduced above, aswell as certain storage of the core (2640) that are of non-transitorynature, such as core-internal mass storage (2647) or ROM (2645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While the particular invention has been described with reference toillustrative embodiments, this description is not meant to be limiting.Various modifications of the illustrative embodiments and additionalembodiments of the invention will be apparent to one of ordinary skillin the art from this description. Those skilled in the art will readilyrecognize that these and various other modifications can be made to theexemplary embodiments, illustrated and described herein, withoutdeparting from the spirit and scope of the present invention. It istherefore contemplated that the appended claims will cover any suchmodifications and alternate embodiments. Certain proportions within theillustrations may be exaggerated, while other proportions may beminimized. Accordingly, the disclosure and the figures are to beregarded as illustrative rather than restrictive.

What is claimed is:
 1. A method for intra bi-prediction and multiplereference line intra prediction in video decoding, the methodcomprising: receiving, by a device comprising a memory storinginstructions and a processor in communication with the memory, a codedvideo bitstream for a block; determining, by the device, whether asingle directional intra prediction or an intra bi-prediction applies tothe block based on mode information of the block, the mode informationof the block comprising at least one of a reference line index of theblock, an intra prediction mode of the block, and a size of the block;in response to determining that the single directional intra predictionapplies to the block, performing, by the device, the single directionalintra prediction to the block; and in response to determining that theintra bi-prediction applies to the block, performing, by the device, theintra bi-prediction to the block.
 2. The method according to claim 1,wherein the determining whether the single directional intra predictionor the intra bi-prediction applies to the block comprises: in responseto the reference line index of the block indicating a non-adjacentreference line, determining that the single directional intra predictionapplies to the block.
 3. The method according to claim 1, wherein thedetermining whether the single directional intra prediction or the intrabi-prediction applies to the block comprises: in response to thereference line index of the block indicating an adjacent reference line,determining that the intra bi-prediction applies to the block.
 4. Themethod according to claim 1, wherein the determining whether the singledirectional intra prediction or the intra bi-prediction applies to theblock comprises: in response to the reference line index of the blockbeing greater than a predefined threshold, determining that the singledirectional intra prediction applies to the block; and in response tothe reference line index of the block not being greater than thepredefined threshold, determining that the intra bi-prediction appliesto the block.
 5. The method according to claim 4, wherein the predefinedthreshold is a non-negative integer.
 6. The method according to claim 1,wherein the determining whether the single directional intra predictionor the intra bi-prediction applies to the block comprises: in responseto the intra prediction mode of the block belonging to a first selectedset of intra prediction modes and the reference line index indicating anadjacent reference line, determining that the intra bi-predictionapplies to the block; in response to the intra prediction mode of theblock belonging to the first selected set of intra prediction modes andthe reference line index indicating a non-adjacent reference line,determining that the single directional intra prediction applies to theblock; and in response to the intra prediction mode of the blockbelonging to a second selected set of intra prediction modes,determining that the intra bi-prediction applies to the block, whereinthe first selected set of intra prediction modes does not overlap withthe second selected set of intra prediction modes.
 7. The methodaccording to claim 6, wherein the second selected set of intraprediction modes comprises a diagonal intra prediction mode.
 8. Themethod according to claim 1, wherein the determining whether the singledirectional intra prediction or the intra bi-prediction applies to theblock comprises: in response to the reference line index of the blockbeing an odd integer and/or the reference line index indicating anon-adjacent reference line, determining that the single directionalintra prediction applies to the block; and in response to the referenceline index of the block being an even integer and/or the reference lineindex indicating an adjacent reference line, determining that the intrabi-prediction applies to the block.
 9. The method according to claim 1,wherein the performing the intra bi-prediction to the block comprises:determining a first predictor based on the reference line index of theblock; determining a second predictor based on the reference line indexof the block; and determining a final predictor for the block accordingto a weighted calculation between the first predictor and the secondpredictor.
 10. The method according to claim 1, wherein the performingthe intra bi-prediction to the block comprises: determining a firstpredictor based on a first reference line index of the block;determining a second predictor based on a second reference line index ofthe block; and determining a final predictor for the block according toa weighted calculation between the first predictor and the secondpredictor.
 11. The method according to claim 10, wherein: the firstreference line index indicates a non-adjacent reference line, and thefirst predictor is generated from a first sample at the non-adjacentreference line; and the second reference line index indicates anadjacent reference line, and the second predictor is generated from asecond sample at the adjacent reference line.
 12. The method accordingto claim 10, wherein the performing the intra bi-prediction to the blockcomprises: the first reference line index indicates a non-adjacentreference line, and the first predictor is generated from a first sampleat the non-adjacent reference line; and the second reference line indexindicates a plurality of reference lines, and the second predictor isgenerated as a linear weighted average of samples, each of which is fromeach of the plurality of reference lines along a prediction angle. 13.The method according to claim 1, further comprising: in response todetermining that the intra bi-prediction applies to the block and thereference line index of the block indicating a non-adjacent referenceline: disabling a reference sample filtering process, in response to areference sample from the non-adjacent reference being available, usingthe reference sample for intra bi-prediction, and in response to thereference sample from the non-adjacent reference being unavailable,using a neighboring available reference sample for intra bi-prediction.14. An apparatus for intra bi-prediction and multiple reference lineintra prediction in video decoding, the apparatus comprising: a memorystoring instructions; and a processor in communication with the memory,wherein, when the processor executes the instructions, the processor isconfigured to cause the apparatus to: receive a coded video bitstreamfor a block; determine whether a single directional intra prediction oran intra bi-prediction applies to the block, based on mode informationof the block, the mode information of the block comprising at least oneof: a reference line index of the block, an intra prediction mode of theblock, and a size of the block; in response to determining that thesingle directional intra prediction applies to the block, perform thesingle directional intra prediction to the block; and in response todetermining that the intra bi-prediction applies to the block, performthe intra bi-prediction to the block.
 15. The apparatus according toclaim 14, wherein, when the processor is configured to cause theapparatus to determine whether the single directional intra predictionor the intra bi-prediction applies to the block, the processor isconfigured to cause the apparatus to: in response to the reference lineindex of the block indicating a non-adjacent reference line, determinethat the single directional intra prediction applies to the block. 16.The apparatus according to claim 14, wherein, when the processor isconfigured to cause the apparatus to determine whether the singledirectional intra prediction or the intra bi-prediction applies to theblock, the processor is configured to cause the apparatus to: inresponse to the reference line index of the block indicating an adjacentreference line, determine that the intra bi-prediction applies to theblock.
 17. The apparatus according to claim 14, wherein, when theprocessor is configured to cause the apparatus to determine whether thesingle directional intra prediction or the intra bi-prediction appliesto the block, the processor is configured to cause the apparatus to: inresponse to the reference line index of the block being greater than apredefined threshold, determine that the single directional intraprediction applies to the block; and in response to the reference lineindex of the block not being greater than the predefined threshold,determine that the intra bi-prediction applies to the block.
 18. Anon-transitory computer readable storage medium storing instructions,wherein, when the instructions are executed by a processor, theinstructions are configured to cause the processor to: receive a codedvideo bitstream for a block; determine whether a single directionalintra prediction or an intra bi-prediction applies to the block, basedon mode information of the block, the mode information of the blockcomprising at least one of: a reference line index of the block, anintra prediction mode of the block, and a size of the block; in responseto determining that the single directional intra prediction applies tothe block, perform the single directional intra prediction to the block;and in response to determining that the intra bi-prediction applies tothe block, perform the intra bi-prediction to the block.
 19. Thenon-transitory computer readable storage medium according to claim 18,wherein, when the instructions are configured to cause the processor todetermine whether the single directional intra prediction or the intrabi-prediction applies to the block, the instructions are configured tocause the processor to: in response to the reference line index of theblock indicating a non-adjacent reference line, determine that thesingle directional intra prediction applies to the block.
 20. Thenon-transitory computer readable storage medium according to claim 18,wherein, when the instructions are configured to cause the processor todetermine whether the single directional intra prediction or the intrabi-prediction applies to the block, the instructions are configured tocause the processor to: in response to the reference line index of theblock indicating an adjacent reference line, determine that the intrabi-prediction applies to the block.